The present invention relates generally to electronic article security-systems for detecting the presence of a security tag within a detection zone and, more particularly, to an improved electronic article security system which provides enhanced reliability over a larger detection zone.
Electronic article security systems for detecting and preventing theft or unauthorized removal of articles or goods from retail establishments and/or other facilities, such as libraries, has become widespread. In general, such security systems employ a security tag which is secured to or associated with an article (or its packaging), typically an article which is readily accessible to potential customers or facility users and, therefore, is susceptible to unauthorized removal. Security tags may take on many different sizes, shapes and forms depending upon the particular type of electronic article security system in use, the type and size of the article to be protected, the packaging for the article, etc. In general, such electronic article security systems are employed for detecting the presence (or the absence) of a security tag and, thus, a protected article within a surveilled security area or detection zone. In most cases, the detection zone is located at or around an exit or entrance to the facility or a portion of the facility.
One type of electronic article security system which has gained widespread popularity utilizes a security tag which includes a self-contained, passive resonant circuit in the form of a small, generally planar printed circuit which resonates at a predetermined detection frequency within a detection frequency range. A transmitter, which is also tuned to the detection frequency, is employed for transmitting electromagnetic energy into the detection zone. A receiver, also tuned to the detection frequency, is positioned proximate to the detection zone. Typically, the transmitter and a transmitter antenna are located on one side of an exit or aisle and the receiver and a receiver antenna are located on the other side of the exit or aisle, so that a person must pass between the transmitter and receiver antennas in order to exit the facility. When an article having an attached security tag moves into or passes through the detection zone, the security tag is exposed to the transmitted energy, resulting in the resonant circuit of the tag resonating to provide an output signal detectable by the receiver. The detection of such an output signal by the receiver indicates the presence of an article with a security tag within the detection zone and the receiver activates an alarm to alert appropriate security or other personnel.
While existing electronic article security systems of the type described above and of other types have been shown to be effective in preventing the theft or unauthorized removal of articles, particularly articles which are relatively high in value and relatively small in size, such systems, due to environmental and regulatory considerations, have a relatively limited range. Typically, the range of such prior art systems is on the order of a maximum of about three feet between the transmitter antenna and the receiver antenna. If the antennas are separated by a greater distance, the reliability of such existing electronic article security systems significantly diminishes. More specifically, as the distance between the transmitter antenna and the receiver antenna increases beyond three feet, the ability of such existing electronic article security systems to accurately detect the presence of a security tag within the detection zone and consistently avoid the generation of "false positives" (generating an alarm when no security tag is present in the detection zone) a high percentage of the time greatly decreases. While, such existing, limited size detection zone electronic article security systems are adequate in applications having limited entrance and exit areas, for example, stores or libraries having only a single entrance door, such systems are not as effective in applications having wide entrance areas or aisles, such as large retail stores having eight, ten or more doors arranged side by side or, in the case of large mall stores, having a generally open area of ten feet or more at the front of the store. Sometimes, in such wide aisle or wide entrance/exit applications, multiple electronic article security systems are connected or networked together in a row across the facility entrance. However, such arrangements sometimes result in congestion and are not aesthetically pleasing.
The present invention comprises an electronic article security system which is particularly well adapted for providing a larger (wider) detection zone (six feet or more) and which function in a very reliable manner.